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Introduction to Antimicrobial Drugs
Antibiotics :^ Substances^ produced by
microorganisms
. which
suppress
the growth of or kill other microorganisms at very low conct. Drug Resistance :
- Can be (^) Natural (^) or
Acquired
.
be due to -
(a) Single step^ mutation (^) ( seen^ with^
Rifampicin
&
(b) streptomycin^ )
Multistep
mutation ( seen with Erythromycin ,^ tetracycline^ )
- Drug Resistance (^) can be transferred (^) from one micro^ -
organism
to other by (^) gene transfer^ .
- Conjugation
- (^) Transduction l Transformation . Mechanism
of
Drug
Resistance :
- (^) Four (^) main mechanisms (^) : iii Drug inactivation (^) or modification
iiii Alteration^ of
Target
site
ciiii Alteration of Metabolic pathway in (^) Reduced drug accumulation.
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are contraindicated^ in^ Renal^ disease^.
- Cephalothin
- Cephaloridine -^ Nitro^ furantoin
- Mali dixie (^) acid
Tetracyclines
( except
doxycycline
( vs Drugs contraindicated in^ liver^ disease^.
Tetracyclines
Pyrazinamide
- Pefloxacin . ( vis^ Genetic Factors^ :^ Antimicrobial^ producing hemolysis in (^) G- GPD deficient (^) patients are^ :
Primaquine
Nitrofurantoin
Chloroquine
- Dapsone
- Quinine - Sulfonamides. C
Classification of Antimicrobial Agents
- Antimicrobials (^) can be classified
a/c to^ several^
ways : TA ] Mechanism^ of Action^ : ii. Drug inhibiting^ cell wall^ synthesis :
iii. Drugs inhibit^ Protein^
synthesis : ciiis Drugs (^) causing leakage^ from^ cell Membrane^ : car Polypeptide Antibiotics (^) : Polymixin B.^
Cole 's tin^.
and tyrothricin
(c) Arabinogalactan (^) synthesis inhibitors (^) : Ethambutol
[ B. ] Based (^) on Type of Action^ : ( is^ Bacteriostatic^ ( (^) stop the growth of bacteria (^) ) in (^) Bactericidal (^) ( kills bacteria ) (c) Based on spectrum (^) of (^) Activity : ( is^ Narrow^ Spectrum -^ Penicillin^ G
, streptomycin^ ,
Erythromycin
in Broad
spectrum
Tetracyclines , chloramphenicol.
Drugs Inhibiting Cell Wall Synthesis - 1
- All^ cell (^) wall synthesis
inhibitors are Bactericidal.
- They are divided into (^) B- lactams &^ non - B lactam drugs.
- P lactam^ antibiotics^ are^ those^ drugs that^ contain
P
ring ,
include : (a) Penicillins (b)
Cephalosporins
(c) Monobactams (d) (^) Carbapenems.
Penicillins
- Mechanism of Action -^ Penicillins^ interact^ with cytoplasmic membrane (^) - binding proteins^ ( PBR^ )^ to inhibit (^) transpeplidation reactions^ involved in crosslinking,^ the^ final step in Cell^ -^ wall^ synthesis .
- (^) Mechanism
of
Resistance :
(a) Penicillin^ ases (^) ( B^ -^ lactamases^ ) break lactam^ ring .
( As^ in
staphylococci
(b) structural changes in PBPS^ of Bacteria^. ( (^) As :^ methicillin -^ resistant
staphylococcus
aureus [ (^) MRSA] , (^) penicillin -^ resistant^ pneumococci.^ ) (c) Changes
in Porin^ structure. ( As^ :^ Pseudomonas )
Resistances /
shortcomings :
(a) Activity
of
Penicillin enhanced if used in combination with P
- (^) lactamase inhibitors. ( clavulanic^ acid^ ,^ sulbactam^ )
- Penicillin^ ✗
(b) Acid Resistant Penicillins :
0 - (^) Oxacillin D- Dicloxacillin [VODKA^ ] K -^ Cloxacillin
A- Amoxicillin
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-^ N^ afcillin and^ Oxacillin^ eliminated^ largely in Bile.
- Ampicillin (^) undergoes Enterobepalic (^) cycling , but excreted
by kidney
.
- Benz (^) a theme penicillin G^ - (^) with (^) 1-1/2--2 weeks (^).
- Side^ effects : (a) Hypersensitivity ( in^ 5-7% He From Urticaria^ skin^ Rash to
Anaphylaxis are^ possible
. (b) GI^ distress^ , (^) esp. Ampicillin
(c) Janisch^ -^ Her^ ✗^ heimer^ Reaction
in treatment^
of syphilis .
Drugs Inhibiting Cell Wall Synthesis - 2 Cephalosporins
- Semi synthetic antibodies (^) derived from cephalosporin^ - (^) C (^).
- Chemically related to
penicillin
.
p
- lactam antibiotics having dihydro^ thiazine ring
( 7-^ amino
cephalosporin
anic acid (^) ).
- (^) All cephalosporins are Bactericidal^.
- Classified into^4 generations :
-^ Most^ enter^ CMS^ :^ important in^ empiric management of^ Meningitis & Sepsis . 1- D^ ]^ Fourth^ Generation :
- Hider^ spectrum
- Resistant to most (^) B- lactamases
- Can enter CMS.
Imipenem & Meropenem
effects :
la > Hypersensitivity
- (^) Incidence 2%
- Rashes &
Drug
Fever
- Positive^ coomb 's Test , but rarely (^) hemolysis
- There is 100% complete Cross reactivity between different (^) cephalosporins & (^) also (^) 5- 10% cross - reactivity with Penicillins.
Ceftazidime is^ implicated
in causing Neutropenia . Carbapenems
- Mechanism of Action^ :
- Same (^) as penicillins and^ cephalosporins
Resistant to p
Spectrum :
- Gram + (^) ve cocci , gram -^ ve^ rods^ &^ anaerobes^.
Important
in - hospital (^) agents for^ empiric use in severe (^) life - threatening infections^ .
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c
Drugs Inhibiting Protein Synthesis - 1
- According to spectrum (^) of Activity. these may be classified as : (a) (^) Broad
Spectrum
:
Chloramphenicol
& Tetracycline (b) Moderate^ Spectrum
: Macrolides & keto tides
(c) Narrow^ spectrum : Lin (^) cos amides (^) , streptogramins and Oxazolidinones^. Mechanism & Site I
